Warm air furnace



Aug. 16, 1966 M ETAL WARM AIR FURNACE I 2 Sheets-Sheet 1 Filed Sept. 23.1965 VENTORS (14/155 f y/14:2

BY (oz/1v 6 Mute %W' ATTO/Q/VE Y6 Aug. 16, 1966 L. G. MILLER ET AL3,266,480

WARM AIR FURNACE Filed Sept. 23, 1965 2 Sheets-Sheet 2 INVENTORS L/4/755M4452 BY [oz/1v GT Mllf/Q Afro/Q A/E Y5 United States Patent 3,266,480WARM AIR FURNACE Lorin G. Miller and James H. Miller, both of 220 S.River, Eaton Rapids, Mich. Filed Sept. 23, 1965, Ser. No. 489,480 3Claims. (Cl. 126-109) The .present invention, which is acontinuation-in-part of our copending application entitled, Warm AirFurnace, Serial Number 299,990, filed on August 5, 1963, which in turnwas a continuation-in-part of application Serial Number 125,690, filedon July 21, 1961, now abandoned, relates to a furnace and moreparticularly to an improved flame chamber for furnaces of the warm orhot air type and which assists in providing compactness, and fueleconomy, and which makes possible furnaces for tight installation as inmobile homes, closet installations as in slab floor houses, and in othercompact dwelling and working space. By reason of substantially completecombustion of organic fuel the structure of the present invention hasbeen utilized as a combination heater and carbon dioxide generator ingreenhouse applications. The unique flame chamber contributes to theunusual combustion efliciency.

The present invention wholly avoids overheating of the furnace outerwalls and in addition, provides about an eighty-five percent efficiencyof heat exchange while rendering the physical structure Olf the furnaceextremely compact. In contrast to prior furnaces, the structuralapproach here taken to provide high efliciency, results in the desiredcompactness and com-fort with attendant safety and economy. The heatexperienced from the use of the presently described structure is veryuniform and easily amenable to simplified thermostatic control since thelocale of the furnace and the elimination of heat directly emanatingfrom the furnace walls does not upset desired uniformity of heatdistribution and balance. These results are accomplished by a simplifiedfire box or flame chamber so that the combustion heat tortuously flowsby the supporting exchange surfaces and so that the flame is shieldedfrom direct exchanger contact and even from radiation contact with theoutwardly facing exchanger surfaces. This arrangement extends the lifeof the tubular exchanger surfaces and a unique mantle liner in the flamechamber accomplishes unusual results in evening heat distribution toboth primary and secondary exchanger surfaces. Collaterally, the bafllemantle, as will be seen, assists in providing an extremely efficientcombustion. Extended testing under severe operating conditions hasindicated minim-a1 exchange surface damage as compared to thatexperienced in many burner units where flame is thrown into directcontact with exchanger surfaces. By reason of substantially completecombustion no residue or soot contaminates the furnace or exchangers.This unusual structure has likewise resulted in minimization offabricating costs since no special metals are required to resistburning. Forced air flow through the exchanger tubes is easily adjustedvolumetrically by conventional control means so that flowing air at nopoint exceeds a maximum set temperature.

The hot air furnace of the present invention is readily convertible fromoil to gas, either natural or bottled, and its efiiciency is independentof the fuel employed. Conditions maintained within the furnace arepositive pressure conditions rendering stack height and negativepressure conditions from the stack less critical and resulting in asuperior utilization of fuel.

In accord with the foregoing, the principal object of the presentinvention is to provide an improved furnace wherein the furnace wallscannot overheat even though they are closely adjoining the exchangesurfaces.

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Another object is to provide a much improved fire chamber and exchangesurface arrangement Within the furnace in shielding the furnace outersurfaces from direct flame or radiation contact.

Another object of the present. invention is to provide a furnaceoperating with a positive pressure in the flame chamber thereby makingthe unit independent of stack height and avoiding negative pressureproblems such as down draft and the like.

Another object is to provide a structure utilizing plural volumetricchokes or constrictions assuring positive pressure conditions in thecombustion chamber and enhancing good heat exchange.

Still another object is to provide a highly efficient and compactfurnace unit for mobile homes and the like which is prepackaged foreconomical installation.

Another object is to provide a chemi-luminescent relatively porous orfibrous mantle-like fire chamber in which combustion is upgraded so thata minimum of fuel residue appears in the exhaust.

Still another object is the provision of a completely pre- Other objectsincluding improved comfort, safety, and

economical performance will be more readily appreciated as thedescription proceeds.

General description In general, a cluster of vertical tubular heatexchange members surround and support a flame chamber. The tubularmembers serve as heat exchanger surfaces with air to be heated passingthrough them. The exchanger tubes are in spaced apart adjacentrelationship and are in adjacent abutting relation to a baffle mantlewhich extends between each of the tubes and faces inwardly toward theflame chamber. This lower and inner baffle mantle extends verticallyabout one-half the length of the exchanger tubes. The outer bafllecommences at the top of the tubes and girdles the tube cluster towardthe outside of the tubes in generally concentric spaced apartrelationship from the lower baffle mantle. The lower baffle mantlecomprises an inorganic fibrous insulating material which glows uponapplication of heat but which is not dependent upon organic binders sothat it serves as an interrupter barrier in preventing flame contactwith the tubes and outer baffle plate as flame is injected into theflame chamber. The refractory material of the bafile mantle is as setforth in US. Letters Patent 3,400,734 to John P. Rex, Jr., et al. Inuse, the baflle mantle glows with a chemiluminosity sulfusing theinterior of the furnace with a radiant form of energy and exposing allprimary exchange surfaces within sight of the baflle mantle. The bafllesare arranged to provide a connected gap between a pair of tubes andthe'flame gun is inserted between selected of the tubes and is aimed todeliver flame to the flame chamber portion defined by the lower bafllemantle. The inner sides of the tube surfaces serve as primary exchangesurfaces and absorb radiant heat from the glowing mantle liner and fromthe rising combustion gases. The rising column of combustion gases isreversed in flow direction by contact with the upper tube support andplenum chamber floor and by the upper and outer baflie so that the gasesare then passed downwardly between the tubes and then upwardly t0 thebacks of the tubes serving as secondary exchange surfaces and then inupward swirling movement to exhaust. Hence, the path of the combustiongases approximates an S form originating in the combustion mantle andtortuously moving to exhaust. The fuel observed underoperating-conditions is impinged upon or in the porous or fibrous mantleelement and the result Patented August 16, 1966 is a very completecombustion with an almost incandescent glow and no observed flame orsmoke.

Several volumetric chokes are seen in the present invention commencingwith the flanged upper edge of the mantle element, the constriction ofgases in motion around and under the outer baflle skirt exchanger tubes,and finally the constriction at the exhaust opening.

The air to be heated is forced through an upper manifold or plenum downthe exchanger tubes, out through a lower manifold and thence to suitableducting. A generally concentric sheath surrounds and is spaced from thetube cluster having a longitudinal partial opening accommodating theflame gun and an opening communicating with the exhaust stack. A ceramicplug aligning the gun may be provided with a pair of access openingstherethrough, a lower gun port and an upper inspection port. Thus, atubular wall is placed about the tube cluster and horizontal tubesupports provide a ceiling and floor closing the furnace while providingvertical communication for warmed air with provisions for separateexhaust of combustible gases.

An outer sheet metal surface or furnace jacket is closely fitted to thewall and provides suitable and decorative mounting means for the flamegun, the stack ducting and automatic controls. No insulation as betweenexchange tubes and walls or jacket is required since by reason of thebaffling no direct contact with flame or radiation occurs. This greatlyminimizes space requirements and is possible because of the eflicientheat exchange. Combustion is sustained by oxygen drawn from the aircoming into the furnace at floor level and the gun is shieded by a guntube and by a ceramic plug or block if desired. Exhaust gases exit abovethe flame gun and on a level approximating the floor of the plenum orfresh air manifold. In operation, a room thermostat (remote from thefurnace) signals the requirement for heat and the burner gun is ignited.The room thermostat, when satisfied, shuts off the gun but the blowercontinues in operation until dissipation of heat from the exchanger. Theblower control is adjustable to maintain proper delivery temperature inthe heated air. From a safety point of view the burner may be shut offwhenever the blower compartment achieves or exceeds a set temperatureand the lower limit switch will break the circuit to the gun iftemperatures at that point achieve or exceed a set temperature. Afurther monitoring control may be used to prevent energization of theburner or gun circuit upon any failure of ignition. While the controlsform no part of the present invention, the general circuitry, well knownin the art, is described in a general manner to indicate the simplicityand adaptability of the present invention to fully automated controlwith safety interlocks.

. During the flame period, the flame chamber is maintained at a positivepressure by volumetric flow adjustment as between flame chamber,secondary heat chamber, and stack entry. This may be viewed assequential orificial constriction.

In the drawing:

FIGURE 1 is a perspectiveview of the furnace of the present inventionand indicating its compact arrangement and indicating in partial brokenline the installation of stack, burner gun, mantle baflle and fire box,exchanger and path of combustion gases.

FIGURE 2 is a perspective view of a group of exchanger tubes and showingthe upper baflles in position and indicating the burner or gun positionin phantom line.

FIGURE 3 is a perspective view of a modified form of exchanger tubecluster with baffles in position.

FIGURE 4 is an exploded view of a furnace in accord with the presentinvention and indicating the principal construction elements and theirinterrelationship.

FIGURE 5 is a full cross section elevation view taken through thestructure as shown in FIGURE 1 and with flow arrows to indicate thedirection of movement of air and combustion gases.

FIGURE 6 is a top elevation cross section taken on the line VI-VI ofFIGURE 5.

FIGURE 7 is a perspective view of a mantle bafile comprising the flamechamber of the present invention and indicating the flanged openingproviding an orificial constriction to combustion gases.

Specific description Referring to the drawing and specifically to FIGURE1, it will be seen that the unit described is extremely compact, thefurnace 11 being rectangular in cross section and having flush sidewalls 12 and back 13. This allows the furnace unit 11 to be directlymounted in a closet or alcove flush against adjacent walls. The facecover 14 is removable and encloses the complete mechanical portion ofthe structure including burner 15, drive 16, jog provisions for stackentry 17, gun port 18 and visual access opening cover 19 A controlpanel, not shown, is also conveniently positionable within the facecover 14. The exhaust stack 20 extends from the upper front portion ofthe furnace 11 and through the cover 21. The cover 21 encloses a blower22 and plenum or air manifold 23 delivering air to be heated downwardlythrough the exchanger tubes 24 as will be seen. A plurality of theexchanger tubes 24 are arranged in a tube cluster and communicate at thetop with the plenum or entry manifold 23 and at the bottom with adelivery chamber or exit manifold 25 connected to warm air deliveryconduit 26. Upper closure plate 27 orients the tubes 24 as does floorplate 28 and the plates 27 and 28 thus define the upper and lower boundsof the heating portion of the furnace 11.

The tubes 24 are clustered concentrically about a flame chamber whichcomprises a mantle bafile 29. Accordingly, the mantle baflle 29 rests onthe floor plate 28 and extends upwardly for about one-half the length ofthe tubes 24 clustered thereabout. The mantle baflle 29 serves to screendirect flame contact from the tubes 24 and, as will be seen, emits achemi-luminescent radiance when fired. The mantle bafile 29 isaccordingly provided with a side entry gun port 30 (see FIGURE 5) and aflanged upper opening 3.1 which provides an orificial first choke onexpanding gases.

An outer tube connecting baflle 32 intermediate each of the tubes 24extends downwardly from the plate 27 to within a relatively shortdistance upward from the floor plate 28. The gap between the lower edge33 of the baffle 32 and the floor plate 28 provides an additional flowconstriction to exhaust gases and serves to separate the tubes 24 intoprimary (inner) exchange surfaces and secondary (outer) exchangesurfaces. The primary (inner) surfaces of the tubes 24 are exposed tothe chemi-luminescen-t glow from the baflle mantle 29. The secondary(outer) surfaces of the tubes 24 are primarily exposed to the partiallyheat stripped gases moving upwardly. An outer encasement 34 surroundsthe tubes 24 and is spaced outwardly therefrom providing an outer upwardpassage for exhaust gases until they exhaust through the stack entry 17in a final volumetric constriction.

The general arrangement of tubes 24 is best appreciated by reference toFIGURE 2 where a rectangular cluster of the tubes 24 is shown. The outerbaffles 32 are shown spacing each of the tubes from the next adjacenttube. The outer baffles 32 extend from the tops of the tubes 24downwardly and the lower edge 33 of the outer baffles 32 stops short ofthe lower ends of the tubes 24. As will be noted, one side of thecluster of tubes 24 is spaced apart by the front plate 35 which, likethe baffles 32, extends downwardly from the upper edge of the tubes 24but terminates slightly below the middle length of the tubes 24 so as toprovide access for the flame gun 15 (phantom line). The front plate 35includes an opening 36 for the visual inspection port 19.

When the gun 15 is finally positioned it is secured in aligned relationby gun tube 37 positioned by gun aperture plate 38 which closes theopening 39 shown in the FIGURE 2. In some instances, it is desirable toutilize a ceramic plug as a centering structure for the nozzle of thegun 15. The outer encasement 34 is provided with the stack entry 17 sothat exhaust gases pass from the interior of the structure and upwardlyinto the exhaust chamber 40 and into the stack 20 as they are trappedbetween the upper closure plate 27, the outer baffles 32, connectedtubes 24, and interior walls of encasement 34. It will be thusappreciated that combustion gases pass from the bafile mantle upwardlyand are then forced downwardly by the upper closure plate 27 and baffles32 in peripheral contact with the inner (primary) exchange surfaces ofthe tubes 24. Then the combustion gases rise in contact with the outer(secondary) exchange portions of the tubes 24 and swirl toward the stackentry 17 moving between the outer baffles 32 and outer encasement 34 andpassing between the front plate 35 and outer encasement 34. Thecombustion gases are thus seen to describe an S pattern of flow in thefurnace 11 and direct flame contact with any surfaces is prevented byconfinement of actual combustion within the mantle bafiie 29. From thecenter of the structure in the baffle mantle 29 gases pass radiallyupward, then downwardly and radially under the skirt formed by thebaffles 32, then upwardly and swirlingly to the front positioned stackentry 17.

As will be appreciated, a variety of forms of tube cluster as well astubes may be utilized and in FIGURE 3 the tubes 24 are cylindricallyarranged in spaced apart vertical grouping with outer baffles 32extending from the upper edge of tubes 24 downwardly as previouslydescribed and clustered about an inner bafile mantle 29'. The frontplate has been removed for clarity and the opening 31 through the tubecluster is shown and also the opening 30 in the baflle mantle 29 asaccess for the flame gun (not shown). No special metals need be usedsince corrosion is substantially avoided by reason of completecombustion in the baffle mantle 29 and 29' and the avoidance of directmetal contact with flame.

In the exploded view of FIGURE 4 the relationship of elements in theFIGURE 1 can be better appreciated. The tube cluster, comprising aplurality of upstanding tubes 24, as seen in FIGURE 2, provides thenecessary exchange capacity and outer bafiling support. The cluster oftubes 24 is positioned and grouped concentrically and in perimetricupright relationship about the inner baflie mantle 29 resting on apalette 41 closing the bailie mantle 29 at the bottom and resting on thefloor plate 28.

The tubes 24 are secured as by swaging or welding in the openings 42 ofthe floor plate 28. The upper closure plate 27 provided with openings 42in register with the tubes 24 is secured to the tubes 24 as in theinstance of the floor plate 28. The upper closure plate 27 is alsoprovided with a semi-circular cut-away front portion 44 foraccommodation of the stack fitting 45. Mated with the stack plate 46,also provided with a semicircular cut-away portion 47, this providesstack support spaced outwardly from the tube cluster and outwardly fromthe front plate 35. This assembly of vertical tubes 24 and outer bafiles32 secured between upper closure plate 27 and floor plate 28 andincluding b-affle mantle 29 is enclosed in the outer encasement 34, theencasement 34 being spaced apart from contact with the tubes 24 andfront plate 35. The stack entry opening 17 at the face of the structureis provided with a jog 40 closing against the upper closure plate 27 andstack plate 46 to provide a communicating passage from the interior tothe stack 20 via the stack fitting 45. Gun tube 37 extending throughaperture plate 38 provides mounting means for the flame gun 15 throughthe front face of the encasement 34. The tube 37 is in registry relationwith the opening 30 in the baffle mantle 29. The visual port cover 19and attached inspection tube 49 is insertable through the registryopening 48 provided through the encasement and above the baffle mantle29. Thus, the opening 48 for the visual inspection cover 19 is in 6register with the corresponding opening 36 in the face plate 35. Theinspection tube 49 is insertable through the openings 48 and 36 forobservation of conditions in furnace 11.

Spaced above the upper closure plate 27 is a chamber top plate 50 havingan opening 51 therethrough for accommodation of the stack fitting 45.The chamber top plate 50 also provides mounting support for the blower22. The blower 22 in its air receiver compartment 52 forces air downwardthrough the chamber top plate 50 and into the plenum chamber 23, throughthe tubes 24 and then to distributing chamber 25 at the bottom of thefurnace structure. -T he vertical spacing between the chamber top plate50 and the closure plate 27 is established by the height of the tubularportion of the fitting 45 and is otherwise bounded by the outer encasingfurnace walls 12 and back 13 and across the front by a panel 53 shown inFIGURE 5.

- By reference to FIGURE 5 the relationship of assembled elements canbest be seen in a full cross section taken on a plane passed front toback through the center of the structure of FIGURE 1 where front as usedherein has reference to the s-ide'of the device through which the flamegun 15 is passed. Combustion occurs wholly within the mantle baflie 29and the mantle achieves a chemi-luminescen-ce at the commencement ofcombustion so that a glow of the mantle occurs throughout the porousmaterial comprising the mantle and which contributes to high combustionefficiency and converts the heat within the structure to a radiantrather than flame contact exposure of primary surfaces. The ignition cfthe incoming fuel is so instantaneous that no definite flame form isvisible, yet the entire baffle mantle 29 produces high energy with nosmoke, residue, or carbon monoxide assuming adequate oxygen fuel ratioat or above stoichiometric requirements for burner and furnace size. Theexhaust gases pass upwardly through the opening 31 in the bafile mantle29 and are constricted in flow by the flange 54 defining the orificialopening 31. Thereupon the combustion gases are permitted to expandvolumetrically upward and outward until confinement by the upper closureplate 27 and the" tube connected outer baffles 32. This forces the gasesdownwardly and around the outer case of the mantle baflie 29 in contactwith the inner facing exposed surfaces of the tubes 24. Then the gasesare again constricted by the gap formed between outer baffles 32 and thefloor plate 28 whereupon the gases again expand and rise in exchangerelation with the outer and secondary faces of the tube 24 and then passforwardly and upwardly in the space between encasement 34 and baffies 32to exhaust through the stack entry 17 and thence upward into the stack20. By reference to FIGURE 1, incoming ambient air is admitted to thechamber 52 through the louvered entry 55 through the face cover 14 andis thereupon forced into the plenum chamber 23 by the action of theblower 22. Upon entry of ambient air to chamber 52, some preheat occursas the incoming air courses around the stack 20 rising verticallythrough the chamber 52. The air in the plenum 23 is heated in passageagainst the upper closure plate 27 and in the tubes 24. Accordingly,that portion of the upper closure plate 27 exposed to the radiant heatsource actually serves as a primary exchange surface. The \balance ofthe closure plate 27 screened from the radiant heat source is asecondary exchange surface. The air to be warmed moves verticallydownwardly through the tubes 24 to the distributing chamber 25 andthence through distributor ducts 26 to points of use remote from thefurnace 11. In FIGURE 6 this relationship is best seen and indicatingthe baffie mantle 29 serving as a flame chamber and as a control bafliefor ex-- panding combustion gases with the flow of air passingdownwardly through the tubes 24. The FIGURE 6 also best shows thepassage of exhaust combustion gases through the stack entry 17 in afinal constriction of the spent gases.

In FIGURE 7 the bafifle mantle 29 is illustrated in perspective and isseen to comprise a molded generally tubular body 56 having an upperflange 54 defining a top opening 31 therethrough and generally axiallypositioned with respect to the body 56.

A transverse opening 31, at right angles to the axis of the body 56opens through the wall of the baffle mantle 29. As will be appreciated,this serves as an aperture for the flame. gun through the gun tube 37.The baflie mantle 29 thus contains all flame and glows with achemiluminescence conducive to complete combustion and places the heatenergy in the most advantageous radiant form for eificient exchange. Itis believed that injected fuel particles impinge on the porous innerWalls of the baffle mantle 29 and are consumed in this position, theradiant heat in the mantle greatly assisting in the achievement ofcomplete combustion. To achieve the desired chemi-luminescence, the baflle mantle 29 is molded from an inorganic fibrous refractory materialhaving a substantial degree of fibrous porosity and held together withan inorganic binder. It may be backed by a metal sheath (not shown) orin thicker material may be free standing as illustrated. Where metalbacking is used, the baflle mantle maintains its chemi-luminescence andprevents direct flame contact with the metal. The material comprisingthe baffle mantle is resistant to heat destruction up to temperatures of4200 degrees Fahrenheit and may be viewed as a refractory shield capableof suifusing heat in a radiant (light) form so as to provide atransmission of heat in a form ready for efficient transfer. Inaddition, the baffle mantle screens all primary surfaces from directflame con-tact thereby extending the life of the furnace and avoidingoxidizing and corrosive destruction of the exchange surfaces.

Operation of the furnace of the present invention is quite unique inthat the flame chamber defined by the baflie mantle 29 is maintainedunder a positive pressure resulting from three constrictions imposedupon the volumetric flow of exhaust gases. The first constriction occursby reason of the flange 54 at the baffle mantle 29. The secondconstriction occurs as the outer baflle arrangement approaches closurewith the floor plate 28. The final constriction occurs at the stackentry 17 and may be modified by additional constrictions in the stack 20as desired. By operating under positive pressure, the furnace 11 inaccord herewith delimits the crit-icality of stack draft and causes anenvironment which upgrades exchange efliciency. This pressuredifferential is of a magnitude of .0204 inch of water above above anambient atmosphere condition. This condition obtains with an input of'14.4 cubic feet/minute to the flame chamber formed by the baflie mantle29 and an exhaust through the flange constriction of 58.7 cubicfeet/minute of expanded gases. Substantially all known furnace deviceshave heretofore been designed to employ a negative pressure in the flamechamber and are accordingly dependent upon highly critical stackconditions for most efficient operation. The device of the presentinvention uses the stack solely as a conduit for spent gases and doesnot rely upon induced: flow for the establishment of a furnaceenvironment of negative pressure, or a pressure below ambient condition.The operation of the described structure is also characterized by a veryslow rise in stack temperature requiring approximately 10 minutes for anelevation of 400 degrees. This is at substantial variance from existingstructures most of which rely heavily upon an induced or forced draftrendering the stack highly critical. This slow rise in stack temperatureis indicative of the highly eflicient exchange or heat utilization.Substantial economies in operation are realizable with the describeddevices.

Test of exhaust gases from furnaces in accord with the foregoingdescription show no carbon monoxide hence indicating a substantiallycomplete combustion varying from 100 percent to the extent of includedsulphur fractions varying largely with particular fuels utilized.Accordingly, devices in accord with the foregoing description haveserved as carbon dioxide generators operating without stack andfavorably received in greenhouse operations where heat and high carbondioxide is sought.

Oxygen for sustaining complete combustion is admitted at the gun 15 Withfuel injected into the baffle mantle 29.

Closest known furnace devices are those of A. T. Lanphere in UnitedStates Letters Patent 173,173 and H. L. De Frees, United States LettersPatent 2,155,968. Both utilize tubular exchangers in a Warm air furnacestructure. Both are understood to rely heavily upon stack conditions foreflicient operation and are accordingly viewed as negative pressurecombustion structures. In United States Letters Patent 173,173 it isunderstood that the flow of air is upward through the tubular exchangersand the baflfling arrangement indicated does not describe thecharacteristic S curve developed by the directed gases in the presentinvention. This is also true of the device of United States LettersPatent 2,155,968, insofar as gas flow direction is concerned, andadditionally, the diagonal bafliing is seen to impose only a U patternto the combustion products. Neither of these known furnaces suggests achemi-luminescent combustion chamber, itself providing a primaryconstriction or choke and serving as a radiant energy filament shieldingdirect flame from ex posure to exchange surfaces.

Excellent exchange efliciencies are found in the described structuresand the efficiency of combustion using the described baflle mantel 29has substantially eliminated the production of carbon monoxide.

Having thus described our invention, it will be appreciated by thoseskilled in the art that various modifications and improvements may beincluded. Such modifications and improvements are intended to beincluded herein limited only by the scope of the hereinafter appendedclaims.

We claim:

1. A flame chamber for positive pressure Warm air furnaces comprising:

(a) a cylindrical inorganic fibrous tube defining a restricted uppermostopening through which combustion gases pass, and closed at the lowermostend and having a transverse opening through the walls thereof andforming a positive pressure choke for generated combustion gases; and

(b) a plurality of spaced apart vertical heat exchanger tubes inconcentric contact arrangement in support of said fibrous tube, saidfibrous tube shielding said exchanger tubes from direct flame contactwhile permitting luminescent heat permeation.

2. A flame chamber for positive pressure warm air furnaces comprising:

(a) a cylindrical inorganic fibrous tube defining a flame chamberserving as a baffle preventing direct flame contact with metal surfacesand including a transverse opening therethrough for the introduction offuel as by a flame gun and a restricted opening at the upper end thereoffor vertical escape of combustion gases; and

(b) a plurality of vertical heat exchanger tubes parallel to the axis ofsaid flame chamber and in support contact therewith, and having theirinwardly facing walls partially in substantial line contact with theouter wall of said flame chamber, said inwardly facing Walls providing aprimary heat exchange surface, and integral outwardly facing tube wallsproviding a secondary exchange surface, said primary surface shieldedfrom flame contact by said flame chamber.

3. A flame mantle for warm air furnaces comprising:

(a) a tubular cylindrical fibrous and porous thin wall flame confiningelement, upon and in the walls of which fuel is impinged for burningthereby converting heat energy to a light form without attendant 9 10flame, the uppermost end of which defines a conopening intersecting thevertical axis of said flame stricted opening and the lower end of whichelement confining element. is closed; (b) a plurality of spaced apartheat exchanger tubes References Cited by the Examiner in verticaladjacent support relationship to said flame 5 confining element, theaxe-s of said exchanger tubes UNITED STATES PATENTS paralleling the axisof said flame confining element; ,6 9,7 2 1/19 9 Balmat 158-4 and,2,117,511 5/ 1938 Scott 122-333 (c) an opening defined transverselythrough the wall of said flame confining element, the axis of said 10JAMES WESTHAVER, Primary Examiner-

1. A FLAME CHAMBER FOR POSITIVE PRESSURE WARM AIR FURNACES COMPRISING:(A) A CYLINDRICAL INORGANIC FIBROUS TUBE DEFINING A RESTRICTED UPPERMOSTOPENING THROUGH WHICH COMBUSTION GASES PASS, AND CLOSED AT THE LOWERMOSTEND AND HAVING A TRANSVERSE OPENING THROUGH THE WALLS THEREOF ANDFORMING A POSITIVE PRESSURE CHOKE FOR GENERATED COMBUSTION GASES; AND(B) A PLURALITY OF SPACED APART VERTICAL HEAT EXCHANGER TUBES INCONCENTRIC CONTACT ARRANGEMENT IN SUPPORT OF SAID FIBROUS TUBE, SAIDFIBROUS TUBE SHIELDING SAID EXCHANGER TUBES FROM DIRECT FLAME CONTACTWHILE PERMITTING LUMINESCENT HEAT PERMEATION.